Casting apparatus for film support or sheeting



April 1952 G. F. NADEAU ETAL CASTING APPARATUS FOR FILM SUPPORT ORSHEETING Filed April 1., 1949 GALE- F. NADEAU ALF M. GLASOE INVENTORS BYW. e

ATTORNEYX Patented Apr. 8, 1952 CASTING APPARATUS FOR FILM SUP- PORT ORSHEETING Gale F. Nadeau and Alt M. Glasoe, Rochester, N. Y., assignorsto Eastman'Kodak Company, Rochester, .N. ,Y., a corporation of NewJersey 1949, Serial No. 85,001

Application April 1,

4 Claims.

The present'invention relates to the art of cast- .ing photographic filmsupport and/or sheeting,

and particularly to an apparatus for casting such film support orsheeting by depositing an evaporative-type dope onto a casting surfaceand obtaining a film or sheet whose surface is free from a wave-likepattern.

In the art of casting film support or transparent sheeting, it is commonpractise to deposit a film of dope of desired thickness onto a movablecasting surface where it is set and cured and finally stripped off thecasting surface in the form of a continuous sheet. Different types ofdopes are used and which require certain modifications in the castingtechnique. For instance, there are dopes known as gel type dopes whichare set by cooling, and are thereafter cured by the circulation of airover the set dope. Dopes of this type require a chilling of the dopeimmediately after deposit on the casting surface, either by cooling thecasting surface or running it through a chillbox. Then there are dopesknown as the evaporative type which require the evaporation or diffusionof a proportion of the solvent contained therein in order for them tobecome set, after 7 which they are further cured to completely removethe contained solvents. It will be understood that since theseevaporative-type dopes remain in a so-called fiuid state for anappreciable time after their deposition on the casting surface,considerable care is required in handling the ,deposited dope up to thetime it is set in order to obtain a film of uniform thickness and,hence, having perfectely smooth surfaces.

Despite all of the exacting steps heretofore taken in the manufacture ofthe casting surface, and the air-circulating systems used in the castingof these evaporative-type dopes, it has been found that very often awavy pattern appears on the surface of the film support or sheet nothaving been engaged by the casting surface. While this wavy pattern isnot too objectionable in some sheeting, it is highly objectionable inphotographic film supports where the uniformity of thickness ofsubsequently coated light-sensitive emulsions is critical, and intransparent sheeting where optical quality is desirable and would bedamaged by a wavy pattern on one of the surfaces of the sheeting.

Accordingly, the primary object of the present invention is to providean improved casting apparatus for handling film dopes of the evaporativetype which reduces, or completely eliminates, the possibility ofobtaining a wavy pattern on the sheet surface as found in some filmsupports and/ or sheeting cast by the use of conventional apparatus.

Another object is to provide an improved casting apparatus of the typeset forth which is so designed as to prevent eddy currents ofcirculating air from contacting that portion of the deposited dope whichis not set sufficiently to resist being worked by such eddy currents ofair, but still allow the solvents to diffuse or evaporate'freely fromthe cast dope.

And, a further object is to provide a casting apparatus of the type setforth in which the freshly cast dope is protected from being directlycontacted by the circulating air through the use of a fine mesh screenwhich is spaced slightly from the surface of the cast dope, and whichallows the solvents to diffuse freely from the cast dope, said screenprotecting the cast dope up to the time said dope is sufficiently set tresist being worked by the circulating air.

The novel features that we consider characteristic of our invention areset forth with particularity in the appended claims. The inventionitself, however, both as to its organization and its methods ofoperation, together with additional objects and advantages thereof, willbest be understood from the following description of specificembodiments when read in connection with the accompanying drawings, inwhich:

Fig. 1 is a side elevational view showing one form of casting apparatusconstructed in accordance with a preferred embodiment of the presentinvention; and

Fig. 2 is an enlarged detailed view of a portion of the apparatus shownin Fig. land showing in detail the protecting screen which is added toconventional casting apparatus in accordance with the present invention.

Like reference characters refer to corresponding parts throughout thedrawings.

In the course of studying the various factors which contribute to thethickness uniformity of a film cast from an evaporative-type dope,either photographic film support or sheeting, we discovered that the airconditions around the green, or uncured, cast dope were of considerableimportance in determining the quality of the final sheet. The mechanismby which variations in the temperature and velocity of the air passingover the uncured dope effect a change in the thickness of it isconsidered to be the result of the velocity of the air at the dope-airinterface on the rate of curing or solvent loss from the dope. We knowthat when the velocity is high, there results a skinning-over of the wetor uncured dope; this skin being subsequently swollen and therebyextended later in the curing process when the air velocity is decreased,so that the rate of removal of solvent at the air-dope interface isrelatively slower than the diffusion of solvent from the body of theuncured dope to the air-dope interface. It is possible in fact todemonstrate this phenomenon on freshly cast dope by the propermanipulation of air currents over its surface. There are small areasvisible on the surface of the dope that show a Wave-like pattern. Thispattern is active if the air currents playing over the dope surfacevary, and it is obvious that this working of the surface of the dopemust necessarily lead to a movement of the viscous dope within the bodyof the cast uncured dope. Such a movement of the'fiowable dope can onlylead to variations in t 'ckness of the finally cured sheet. It ispossible to see these effects in various ways by means of properlydesigned experiments, and it is also possible to show that air velocityand eddy currents are not eifective in producing such thicknessvariations on a dope that is gelled or set on contact with the castingsurface, and thereby render it immobile.

By reason of the fact that, from a practical standpoint, it has not beenpossible to design a casing around a dope casting surface, whether it bea wheel or band, of sufiicient accuracy and of the proper geometricalproportiorm to assure absolute uniformity of air flow across the widthof a normal casting wheel or band, we have approached and solved theproblem in another manner. We first visualized that if the solvent couldbe removed uniformly over all of the surface of the cast dope by somediffusion process, free of the rapid and non-uniform movement of largebodies of air, a more nearly uniform rate of evaporation would resultthereby in a film of more uniform thickness.

We discovered that such a condition could be realized by fixing arelatively fine screen parallel to the casting surface and approximatelyone inch therefrom; said screen being located adjacent the point ofdeposition of the dope on the casting surface. With this apparatus,variations in the velocity of air flow over the screen (eddy currents)did not result in the working of the dope which normally occurred if thedope surface was exposed to such eddy currents, or other non-uniform airflow. Under these conditions the solvent diffuses out of the dope andthrough the screen, the movement of the curing air over the screeneffectively maintaining a low and safe solvent concentration. Since thecuring process is primarily one of diffusion, the above-describedprocedure does not reduce the rate of curing of the dope.

Referring now to the drawing wherein a specific embodiment of thepresent invention is shown in association with one form of conventionalcasting apparatus represents a large casting wheel, onto the surface ofwhich a regulated film of evaporative-type dope I l is fed from a hopperl2. The casting wheel I0 is rotated by any suitable drive means, notshown, in a clockwise direction at a speed dictated by its size, thenature of the film dope, and the curing effect of the air circulationsystem, so that when the deposited film of dope reaches stripping rolll3, the completely cured sheet S can be stripped from the wheel andpassed over guide rollers M to a take-up roll, or other apparatus, notshown. In order to effect the desired curing of the cast film of dope onthe wheel, it is customary to circulate air, warmed or otherwise,depending upon the nature of the dope, in a carefully regulated mannerover the casting surface, so as to try to eliminate deformation of theuncured film of dope on the wheel. In the embodiment disclosed this isaccomplished by enclosing the wheel surface with a casing I6 which isconcentric to and substantially spaced from the wheel surface to reduceany tendency to produce a high velocity of air over the wheel surface.One end of this casing is connected to an inlet pipe I! through whichair, under pressure, may be fed to the casing by a pressure fan, orother suitable means, not shown. The other end of the casing isconnected to an outlet pipe l8 which is, in turn, associated by anexhaust fan 19. Accordingly, the air flow through the casing is asindicated by the arrows in Fig. 1, or through the casing I6 in adirection counter to the direction of movement of the wheel surface.

All of the apparatus described'up to this point is conventional andforms no part of the present invention pre se, except as it acts incombination with, or is modified by, the new and novel structure to behereinafter described. It will be obvious that the type of castingapparatus to which applicants invention is applied need not be .of thewheel-type, as disclosed by way of illustration, but that it couldlikewise be a casting apparatus using a band-type of casting surfacealong with any other suitable type of dope-depositing means and anyother suitable type of air-circulating system.

Coming now to the present invention we fix a fine mesh screen 20 in withthat portion of the casting surface adjacent the point at which the dopeis deposited thereon and extending along the casting surface from thepoint of application of the dope to the point on the surface at whichthe cast film of dope is suificiently set, or cured, 'to resist being"workecl by eddy currents or non-uniform velocity in the circulating airpassing over that portion of the casting surface. The term worked asused means that the cast film of dope is sufficiently uncured, or unset,to possess a mobility which would permit eddy currents or changes in thevelocity of air moving thereover to cause the entire body, or at leastthe surface thereof, to be physically disturbed to produce a wavy orirregular surface. As shown. this screen 20 is fixed at one end to thewall of the hopper and is arcuate in shape so as to extend parallel tothe casting surface of the wheel. This screen 20 is wide enough to coverthe entire width of the casting surface, and the length of the uncureddope that should be protected by such screen is variable and is more orless specific for each dope, depending upon its rate of setting, thespeed of the casting surface. etc. However, for most of theevaporative-type dopes now being currently used in the film-support art,a screen eight feet long appears to be sufficient. For a dope that setsfairly rapidly, this length could be reduced to as little as three feet.

We have found that a screen located relative to the casting surface asdescribed prevents any eddy currents of air formed by variations in thevelocity of air flowing over the screen from "working the dope. On theother hand, as illustrated in Fig. 2 by directional arrows, this screenallows the solvent in the dope to diffuse out of the dope as readily asif the screen were not present, and the movement of the curing spacedparallel relation air over the screen effectively maintains a low andsafe solvent concentration in the air casing I6 and associated outletpipe 18. Since the curing process of the dope is primarily one ofdiffusion, the introduction of this screen does not reduce the rate ofcuring of the dope.

The size of the screen mesh is definitely less critical than the lengthof the screen, since it is only necessary that the mesh be fine enoughto prevent passage of large volumes of directed air into contact withthe cast dope. In experiments we have conducted, screen sizes of 30 and60 mesh have been used with approximately equal results. It is ourconclusion that the limits as to screen size are 20 to 100 mesh, sinceanything finer than 100 mesh appears to prevent adequate diffusion ofthe solvent from the dope and unduly reduces the curing rate, while anymesh coarser than 20 fails to prevent the passage of large volumes ofdirected air into contact with the fresh-cast dope which are conduciveto undesirable eddy currents.

With respect to the placement of the screen relative to the depositeddope surface, we feel that although not critical, however for practicalreasons the screen should be substantially parallel with the castingsurface and be placed approximately one inch above the dope being cured.Closer placement of the screen has been found to be impractical becauseof mechanical difficulties and although the screen might be positionedtwo or three inches above the dope, there is no practical reason fordoing so.

While we have shown the screen 20 associated with a casting wheel andmounted by being fixed at one end to the wall of the dope hopper 12, it

will be readily understood that a screen of this type could beassociated with any type of casting surface and dope depositing meanswithin the spirit of the present invention, since the purpose andfunction of the screen is not limited by its individual shape or itsmanner of mounting. Inasmuch as evaporative-type film dopes are many andwell-known in the art, and the present invention is not limited to theuse of any one thereof, it is not deemed necessary to elaborate on themanufacture, the composition, or other characteristics of these dopes.However, to give one example of a known film dope of the evaporativetype which a casting apparatus, constructed in accordance with thepresent invention, is adapted to handle, we might mention a dopecomposed of one part cellulose acetate, two and one-half to three partsacetone, plus a desired quantity of a suitable plasticizer, forinstance,

25 per cent diethyl phthalate based on acetone. A dope of this type isgenerally coated at a temperature between -130 F., preferably F.

Although we have shown and described certain specific embodiments of ourinvention, we are aware that many modifications thereof are possible.Our invention therefore is not to be limited to the precise details ofconstruction shown and described but is intended to cover allmodifications coming within the scope of the appended claims.

Having thus described our invention, what we claim is new and desire tosecure by Letters Patent of the United States is:

1. A sheet casting apparatus comprising a movable casting surface, ahopper for depositing a uniform thin film of evaporative-type dope ontosaid casting surface, means for circulating air over that portion of thecasting surface carrying said deposited dope to evaporate and cure thesame, and a fine mesh screen, independent of said last-mentioned means,extending from the hopper in the direction of movement of the castingsurface and being disposed in parallel spaced relation with said castingsurface to prevent eddy currents in the circulating air from directlycontacting the film of dope of said casting surface and to permit thedope to evaporate due to a diffusion action, said screen being longenough to cover that portion of the casting surface up to the pointwhere the dope is sufficiently set to resist being worked by thecirculating air passing over said casting surface.

2. A sheet casting apparatus according to claim 1 in which the screen isone between 20 and 100 mesh.

3. A sheet casting apparatus according to claim 1 in which the screen islong enough to extend at least three feet along the casting surface fromthe point of application of the dope.

4. A sheet casting apparatus according to claim 1 in which the screen isspaced within two inches of the casting surface.

GALE F. NADEAU. ALF M. GLASOE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,045,328 Levey June 23, 19362,161,356 Jewett June 6, 1939 2,252,684 Babcock Aug. 19, 1941

